Device for the diffusion and distribution of high frequency energy in a resonant cavity for preheating and baking of non-metallic materials and the like



Oct. 21, 1969 J. H. A. SOULIER 3,474,211

DEVICE FOR THE DIFFUSION AND DISTRIBUTION OF HIGH FREQUENCY ENERGY IN A RESONANT CAVITY FOR PREHEATING AND BAKING OF NON-METALLIC MATERIALS AND THE LIKE Filed Aug. 14, 1967 INVEN T R n F5 3 7 J'OEL H. A. SOULIER y u y A ls United States Patent Int. or. 1323]; 9/06 US. or. 219-1055 10 Claims ABSTRACT OF THE DISCLOSURE The diffusion and distribution of UHF energy in a resonant cavity defined by a parallelepiped enclosure is effected by a wave guide casing opening into the cavity through at least one of the enclosure walls. The lateral wall of the casing facing the cavity is formed as a parabola and the antenna of a wave generator projects into the casing at the focus of the parabola. At least one phasedisorganizing element is provided within the casing between the antenna and the opening into the cavity. The element is in the form of a disc having concentric steps and radial slots.

The present invention relates to an improved device for the diffusion of high frequencies between 40 and 2,500 megahertz within curing cavities such as ovens. In the following, those frequencies will be called UHF frequencies.

It is known to use such UHF waves for thermal curing of various materials and products, for example for food cooking. Up to now, however, it has been difficult to cure large quantities of pasty materials homogeneously, because UHF waves are not homogeneously and uniformly distributed everywhere Within the curing cavities.

According to the invention, the waves produced by an UHF generator are emitted in the neighborhood of the focus of parabolic reflector directed towards said cavity.

The oven of the invention comprises a parallelepiped enclosure of which at least one of the walls is provided to support a casing internally related with said enclosure, said casing being of a rectangular crass section and having a parabolic lateral wall, a wave generator being moreover coupled with said casing by way of an antenna protruding therein and disposed at the focus of the parabola defined by its lateral wall, so that this casing constitutes a wave guide.

Various other features will be revealed from the following detailed description, with reference to the accompanying drawing representing in an illustrative and by no means limitative manner some embodiments of this invention.

In the drawing:

FIG. 1 is a diagrammatic perspective view of an oven illustrating an embodiment of the invention.

FIG. 2 is a diagrammatic fragmentary elevation of an oven with parts broken away showing another embodiment of the invention.

FIG. 3 is a diagrammatic fragmentary cross-section taken along line III-III of FIG. 2.

FIG. 3a! is a diagrammatic fragmentary cross-section taken along line IIIa-Illa of FIG. 2 and shows a detail of the invention.

FIG. 4 is an enlarged elevation of a detail of FIG. 1.

FIG. 5 is a cross-section taken along line VV of FIG. 4.

In the embodiment accordinf to FIG. 1, the oven comprises an enclosure 1 defining a cavity, the internal wall of which is made from a material known for reflecting UHF waves produced by a generator 2 known per se, a magnetron by way of example. The enclosure 1 is represented as being a parallelepiped and is closed on one of its side by a door 3.

The UHF waves produced by said generator 2 are emitted by an antenna 4 provided within a casing 5 acting as a wave guide, said casing being connected with the inside of the cavity defined by the enclosure 1.

The lateral wall 5a of the casing 5 is parabolically shaped and the walls of said casing are made of a material which reflects UHF waves so to direct said waves inside the cavity defined by the enclosure 1 in which materials or products to be submitted to thermal curing are disposed.

FIGS. 2 and 3 show an oven similar to that of FIG. 1, but in which the cavity defined by the enclosure 1 is sub jected to the action of three wave guides. The wave guide casings 5, 5 5 are supported by three of the enclosure walls so that the enclosure cavity is traversed by wave beams according to the three cartesian coordinates, said three casings 5, 5 5 each having a parabolically shaped lateral Wall.

The drawing shows that the casings 5, 5 5 used as wave-guides contain devices, hereinafter called shifters, to dephase and disorganize the phase. These shifters 6 and 7 are disposed in each casing. The shifters may occupy less than the height of the casing-s as diagrammatically shown in FIG. 3 or, as shown in FIG. 3a, they may occupy all the height of the casing. Each shifter, as shown in FIGS. 4 and 5 is in the form of a disc 8, one side of which is shaped so as to present concentric notches or steps 9 disposed in successive parallel planes. Each disc is further provided with a plurality of radial slots 10, said slots being symmetrically disposed as shown. The width of the slots is determined so to constitute a resonant window for the UHF waves emitted from the antenna 4 of each generator 2.

In a preferred form of embodiment, the disc of the shifter has an outer diameter of mm. and a thickness of 42 mm., and is provided with three concentrical notches or steps equidistantly disposed are provided therein, each step being 14 mm. high. Additionally, three resonant slots 10 are provided in equally spaced relation, each slot having a depth of 65 mm. and a width of 31 mm.

The discs 8 are made from a material having low dielectric losses for UHF waves, so that those waves may travel through said discs, while being subjected to a refraction which varies according to the notch or step through which the incident ray of the wave enters and also according to the notch or step through which each ray exists.

It has been experimentally found that it is advantageous to provide two of said shifters inside of each wave guide and to place those shifters so that the center of each disc is approximately in coincidence with the secondary foci of interference, which originate in said wave guides approximately at the points designated by a and b in FIGURE 2 when the antenna 4 of generator 2 is placed at the focus of the parabola defined by the wall 5a of each wave guide.

To improve the effect further, it has been found advantageous, as shown in FIGS. 3 and 5, to support the disc 8 on a shaft 11 driven by an electric motor 12 rotating at a speed of about 3,000 r.p.m. Moreover, the two shifters 6 and 7 are preferably aligned initially so that the slots 10 of the two shifters successively register as is shown in FIG. 2.

With the arrangement as above described, it is possible continuously to vary the phase of the radiation emitted from the antenna 4 of each wave guide to insure an homogeneous distribution of the radiation inside the cavity defined by the enclosure 1.

To increase the homogeneous distribution of the energy inside the cavity 1 even further, it is advantageous to mount the two shifters disposed in each wave guide in opposition. That is to say, to dispose the disc 8 of one shifter, for example shifter 6, so that its top be directed upwardly, while the disc 8 of the other shifter is disposed so that its top is directed downwardly.

As shown in FIG. 2, the wave guide casing may be oriented in such a manner that the plane P perpendicular to the antenna 4 is inclined at an angle a with respect to the corresponding coordinates axis of the enclosure cavity. The angle a of inclination generally lies between and 30 and prevents wave reflection from disturbing the functioning of the Wave guide and that of its associated generator 2.

The material which is to be thermally cured, for examplc a mass of raw rubber or various synthetic materials, is placed within the cavity and said mass 13 or masses, as shown in FIG. 2, is disposed on one or more plates 14 driven by a motor 15 at a rotational speed of about 10 to rpm. Owing to this procedure, homogeneous and uniform heating of all the bulk of material 13 is effected regardless of the shape and the nature of said bulk.

In simplified devices, only one shifter may be used, in which case, the shifter is roughly aligned with the antenna 4 along the axis of the parabola delimited by the wall 50 of each wave guide.

I claim:

1. A device for the diffusion and distribution of UHF energy in a resonant cavity for preheating and baking non-metallic materials and the like, said device comprisng a parallelepiped enclosure defining the cavity, a casng defining a wave guide communicating with said cavity, said casing having a parabolic lateral wall falling said cavity and being of rectangular cross section, an antenna projecting into said casing at the focus of the parabola defined by said lateral wall, a wave generator connected to said antenna, at least one phase-disorganizing member within said casing, said member being in the form of a disc having one side thereof provided with concentric notches or steps, said disc also having a plurality of radially disposed slots constituting resonant windows.

2. A device for the diffusion and distribution of UHF energy in a resonant cavity for preheating and baking non-metallic materials and the like, said device comprising a parallelepiped enclosure defining the cavity, a casng defining a wave guide communicating with said cavity, said casing having a parabolic lateral wall facing said cavity and being of rectangular cross section, an antenna pro ecting into said casing at the focus of the parabola defined by said lateral wall, a wave generator connected to said antenna, a pair of phase-disorganizing members with said casing, said members being symmetrically disposed on opposite sides of the axis of the parabola formed of said lateral wall and between the focus of said parabola and the opening of said casing into the enclosure.

3. Device according to claim 2 wherein the two discs constituting the shifters are mounted in an opposed manner inside the wave guide casing.

4. A device for the diffusion and distribution of UHF energy in a resonant cavity for preheating and baking non-metallic materials and the like, said device comprising a parallelepiped enclosure defining the cavity a casing defining a wave guide communicating with said cavity, said casing having a parabolic lateral wall facing said cavity and being of rectangular cross section, an antenna projecting into said casing at the focus of the parabola defined by said lateral wall, a wave generator connected to said antenna, said wave guide casing being obliquely disposed with respect to the edge of the wall of the supporting enclosure.

5. Device according to claim 4 wherein the angle made by the casing and the edge of the supporting wall is between 15 and 30.

6. A device for the dilfusion and distribution of Ul-IF energy in a resonant cavity for preheatingand baking non-metallic materials and the like, said device comprising a parallelepiped enclosure defining the cav1ty, a casing defining a wave guide communicating with said cavity, said casing having a parabolic lateral wall facing said cavity and being of rectangular cross section, an antenna projecting into said casing at the focus of the parabola defined by said lateral wall, a wave generator connected to said antenna, the enclosure being provided with three identical casings on adjacent side walls thereof.

7. A device for the diffusion and distribution of UHF energy in a resonant cavity, for preheatingand baking non-metallic materials and the like, said device comprising a parallelepiped enclosure defining the cav1ty, a casing defining a wave guide opening into said cav1ty, sald casing being of a rectangular cross section and having a parabolic lateral wall, an antenna pro ecting nto said cavity at the focus of the parabola define d by said lateral wall, a wave generator coupled with said antenna, protruding therein and disposed at the at least one phaseshifting element inside the casing and belng made of a low dielectric loss material for the UHF waves, said element being in the form of a disc having one side thereof provided with concentric notches or steps.

8. A device according to claim 7 wherein the disc 15 also provided with radially extending slots constituting resonant windows.

9. A device according to claim 7 including means for rotating said disc about its axis.

10. Device according to claim 7 including a plate provided inside the enclosure to support the mater1als or products to be thermally cured, and means for rotatlng said plate.

References Cited UNITED STATES PATENTS 2,255,042 9/1941 Barrow 343786 2,304,540 12/1942 Cassen 333-83 X 2,272,839 2/1942 Hammond 343-840X 3,300,615 1/1967 Smith 219-1055 3,373,259 3/1968 Smith 2l910.55

FOREIGN PATENTS 1,092,484 11/ 1967 Great Britain.

JOSEPH V. TRUE, Primary Examiner L. H. BENDER, Assistant Examiner 

